Notes

Abstract:

The objective of this study was to conduct a titration study using ractopamine-HCl during the last 30 days of feeding to determine if muscle mass could be increased in mature cows. Effects on meat quality of selected muscles and muscle fiber histological changes were studied. Culled crossbred beef cows (n = 98) representing two breed types (Beefmaster and Angus type) were randomly sorted based on breed type into one of four pens and fed for 54 days on concentrate feed, and assigned to one of four treatment groups: Control fed, OptaflexxTM at 100, 200, or 300 mg/hd/day. Except for the control, experimental groups received OptaflexxTM during the last 30 days of the 54 day feeding trial. At 24 hours post harvest, the carcasses were fabricated and nine muscles adductor (ADD), gracilis (GRA), infraspinatus (INF), longissimus (LM), rectus femoris (REF), semimembranosus (SMB), teres major (TEM), triceps brachii (TRBLAT, TRBLONG), and vastus lateralis (VAL) were removed, weighed, measured, and aged in cryovac B2570 (Sealed Air Corp., Duncan, SC) vacuum bags for 14 days. The 9-10-11 rib section was removed for compositional analysis. Warner-Bratzler shear force (WBSF) was performed on all muscles. Ether extraction of lipids was performed on a sample of the LM to determine percent intramuscular fat. Data were analyzed using the MIXED procedure of SAS utilizing animal as the experimental unit. Significance was determined at P < 0.05. Hot carcass weight tended (P = 0.14) to be lower for the 100 mg/hd/d group compared to the control. Dressing percent tended (P = 0.19) to be lower for the 200 mg/hd/d group compared to the control. There were no differences in ribeye area, or percent intramuscular fat. There was a trend (P = 0.11) for percent fat-free lean to increase as ractopamine-HCl dose increased. Ractopamine-HCl had minimal effects on meat tenderness overall for the nine muscles evaluated. The 200 mg/hd/d VAL type I fiber increased in cross sectional area and diameter. SMB and VAL fibers underwent a fiber-type shift from type I fiber to type II fiber in the 200 mg/hd/d group. In conclusion, feeding ractopamine-HCl at the 100, 200, or 300 mg/hd/d level to cull beef cows has little to no effect on carcass characteristics in comparison to feeding with the exclusion of ractopamine-HCl, but ractopamine did have some minimal effects on total fat-free lean percentage and WBSF values. An unexpected histological change was observed in muscle fiber which has not been reported in cull cows treated with ractopamine-HCl.

General Note:

In the series University of Florida Digital Collections.

General Note:

Includes vita.

Bibliography:

Includes bibliographical references.

Source of Description:

Description based on online resource; title from PDF title page.

Source of Description:

This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.

Notes

Abstract:

The objective of this study was to conduct a titration study using ractopamine-HCl during the last 30 days of feeding to determine if muscle mass could be increased in mature cows. Effects on meat quality of selected muscles and muscle fiber histological changes were studied. Culled crossbred beef cows (n = 98) representing two breed types (Beefmaster and Angus type) were randomly sorted based on breed type into one of four pens and fed for 54 days on concentrate feed, and assigned to one of four treatment groups: Control fed, OptaflexxTM at 100, 200, or 300 mg/hd/day. Except for the control, experimental groups received OptaflexxTM during the last 30 days of the 54 day feeding trial. At 24 hours post harvest, the carcasses were fabricated and nine muscles adductor (ADD), gracilis (GRA), infraspinatus (INF), longissimus (LM), rectus femoris (REF), semimembranosus (SMB), teres major (TEM), triceps brachii (TRBLAT, TRBLONG), and vastus lateralis (VAL) were removed, weighed, measured, and aged in cryovac B2570 (Sealed Air Corp., Duncan, SC) vacuum bags for 14 days. The 9-10-11 rib section was removed for compositional analysis. Warner-Bratzler shear force (WBSF) was performed on all muscles. Ether extraction of lipids was performed on a sample of the LM to determine percent intramuscular fat. Data were analyzed using the MIXED procedure of SAS utilizing animal as the experimental unit. Significance was determined at P < 0.05. Hot carcass weight tended (P = 0.14) to be lower for the 100 mg/hd/d group compared to the control. Dressing percent tended (P = 0.19) to be lower for the 200 mg/hd/d group compared to the control. There were no differences in ribeye area, or percent intramuscular fat. There was a trend (P = 0.11) for percent fat-free lean to increase as ractopamine-HCl dose increased. Ractopamine-HCl had minimal effects on meat tenderness overall for the nine muscles evaluated. The 200 mg/hd/d VAL type I fiber increased in cross sectional area and diameter. SMB and VAL fibers underwent a fiber-type shift from type I fiber to type II fiber in the 200 mg/hd/d group. In conclusion, feeding ractopamine-HCl at the 100, 200, or 300 mg/hd/d level to cull beef cows has little to no effect on carcass characteristics in comparison to feeding with the exclusion of ractopamine-HCl, but ractopamine did have some minimal effects on total fat-free lean percentage and WBSF values. An unexpected histological change was observed in muscle fiber which has not been reported in cull cows treated with ractopamine-HCl.

General Note:

In the series University of Florida Digital Collections.

General Note:

Includes vita.

Bibliography:

Includes bibliographical references.

Source of Description:

Description based on online resource; title from PDF title page.

Source of Description:

This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.

Young, 1998). An improvement in carcass characteristics creates value in the boneless

subprimals, which would expand the carcass marketing options, currently restricted to ground

beef and sausage manufacturing (Hilton et al., 1996).

CHAPTER 2
LITERATURE REVIEW

Forage Diet

Brown and Johnson (1991) examined the effects of energy and protein supplementation of

ammoniated tropical grass hay on the growth and carcass characteristics of cull cows. During

trial 1, which had a feeding period of 118d, 56 Brahman crossbred cows were assigned to one of

four treatments:

* The control group which was slaughtered at the beginning of the trial to determine initial
carcass characteristics
* Ammoniated hay alone
* Ammoniated hay plus 2.2 kg dry matter (DM) of liquid cane molasses per day
* Ammoniated hay plus 2.2 kg DM of citrus pulp per day

The feeding trial was repeated using different protein sources. This experiment lasted

1 10d, and used 63 Brahman crossbred cows were assigned to one of four treatments:

* The control group which was slaughtered at the beginning of the trial to determine initial
carcass characteristics
* Ammoniated hay alone
* Ammoniated hay plus 3.4 kg DM of liquid cane molasses per day
* Ammoniated hay plus 2.9 kg DM of liquid cane molasses plus 0.5 kg DM of cottonseed
per day

The cows were conditioned to the diets for four days and were weighed for three

consecutive days at the beginning and end of the trial. Cows fed strictly ammoniated hay

consumed a large amount of hay (approximately 3% of their BW). Supplementation of citrus

Baseline excluded from statistical analysis. Means were rounded to the nearest tenth. 1Live
weight measured in Kg. 2 Hot carcass weights measured in Kg. 3 Dressing percentage. ,b Means
in the same row with different superscripts differ at (P=0.14). X'y Means in the same row with
different superscripts differ at (P=0.19).

AMSA. (1995). Research guidelines for cookery, sensory evaluation, and instrumental
tenderness measurements of fresh meat. American Meat Science Association in
cooperation with the National Live Stock and Meat Board, now the National
Cattleman's Beef Association, Centennial, CO.

FEEDING OPTAFLEXX TM 45 (RACTOPAMINE-HCL) TO CULL COWS: EFFECTS ON CARCASS COMPOSITION, YIELD, WARNER-BRATZLER SHEAR FORCE AND MUSCLE HISTOLOGY TRAITS By RYAN DIJKHUIS A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2007 1

PAGE 2

2007 Ryan Dijkhuis 2

PAGE 3

To my parents. Thanks for standing behind me. 3

PAGE 4

ACKNOWLEDGMENTS It is obvious that many people played a role in my education and it would be hard to thank every imaginable person, so I would like to start off by thanking every teacher who has influenced me and my education. Of course I would also like to thank my family, Mom, Dad, Meg, Grandma, Grandpa, and Cree and Dennis for supporting me throughout this entire process. Along the lines of family I would also like to thank my wife Amy and her family for endless support. Amy you are the best wife a guy could ask for, thanks for spending weekends with me freezing your butt off in the cooler when I had to cut all my steaks, you do not know how big of a help you were and how much I appreciate that. Also I would like to thank Amy for supporting all of my dreams and goals that I want to achieve in our life. I would also like to thank my fellow graduate students and office mates John Michael Gonzalez and Brian Sapp. If it were not for them I would be up the creek with out a paddle. I would like to thank John for all your work in the lab with the histology aspect of the project and for always letting me borrow your digital camera. I know University of Florida department of Animal Sciences will keep your name on their rolodex (do those things still exist?) because you definitely know your stuff. Brian thanks for all the help in the kitchen and lab when I had to cook and shear all those steaks, you were a life saver. I could not ask for a better bunch of guys than those two, thanks for some great times in the office. Larry Eubanks, he was like a second dad to me throughout my entire college career at the University. He taught me many things, kept me humble, and supported me day in and day out, whether it was through food or wisdom. I would also like to thank the guys at the meat lab, Byron Davis and Tommy Estevez; I can not even begin to describe the amount thanks I owe to them. They were the best guys to work for and work with; they taught me so much and really opened my eyes and help me find my love for the meats field. I would also like to thank those two guys for all the help in the cutting room during this project, even though I said I could do it 4

PAGE 5

myself I knew I needed their help, but its fun to give Byron a hard time. Finally I would like to thank my committee members Dr. Sally Johnson, Dr. Sally Williams, and the one person who made all this possible for me, and that is Dr. Dwain Johnson, my major professor. I could not have asked to do my work under a better person than him. I Thank Doc for taking me on as a graduate student and letting me achieve my academic goals. 5

Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science FEEDING OPTAFLEXX TM 45 (RACTOPAMINE-HCL) TO CULL COWS: EFFECTS ON CARCASS COMPOSITION, YIELD, WARNER-BRATZLER SHEAR FORCE AND MUSCLE HISTOLOGY TRAITS By Ryan Dijkhuis August 2007 Chair: Dwain Johnson Major: Animal Sciences The objective of this study was to conduct a titration study using ractopamine-HCl during the last 30 days of feeding to determine if muscle mass could be increased in mature cows. Effects on meat quality of selected muscles and muscle fiber histological changes were studied. Culled crossbred beef cows (n = 98) representing two breed types (Beefmaster and Angus type) were randomly sorted based on breed type into one of four pens and fed for 54 days on concentrate feed, and assigned to one of four treatment groups: Control fed, Optaflexx TM at 100, 200, or 300 mg/hd/day. Except for the control, experimental groups received Optaflexx TM during the last 30 days of the 54 day feeding trial. At 24 hours post harvest, the carcasses were fabricated and nine muscles [adductor (ADD), gracilis (GRA), infraspinatus (INF), longissimus (LM), rectus femoris (REF), semimembranosus (SMB), teres major (TEM), triceps brachii (TRB LAT, TRB LONG ), and vastus lateralis (VAL)] were removed, weighed, measured, and aged in cryovac B2570 (Sealed Air Corp., Duncan, SC) vacuum bags for 14 days. The 9-10-11 rib section was removed for compositional analysis. Warner-Bratzler shear force (WBSF) was performed on all muscles. Ether extraction of lipids was performed on a sample of the LM to determine percent intramuscular fat. Data were analyzed using the MIXED procedure of SAS 10

PAGE 11

utilizing animal as the experimental unit. Significance was determined at P < 0.05. Hot carcass weight tended (P = 0.14) to be lower for the 100 mg/hd/d group compared to the control. Dressing percent tended (P = 0.19) to be lower for the 200 mg/hd/d group compared to the control. There were no differences in ribeye area, or percent intramuscular fat. There was a trend (P = 0.11) for percent fat-free lean to increase as ractopamine-HCl dose increased. Ractopamine-HCl had minimal effects on meat tenderness overall for the nine muscles evaluated. The 200 mg/hd/d VAL type I fiber increased in cross sectional area and diameter. SMB and VAL fibers underwent a fiber-type shift from type I fiber to type II fiber in the 200 mg/hd/d group. In conclusion, feeding ractopamine-HCl at the 100, 200, or 300 mg/hd/d level to cull beef cows has little to no effect on carcass characteristics in comparison to feeding with the exclusion of ractopamine-HCl, but ractopamine did have some minimal effects on total fat-free lean percentage and WBSF values. An unexpected histological change was observed in muscle fiber which has not been reported in cull cows treated with ractopamine-HCl. 11

PAGE 12

CHAPTER 1 INTRODUCTION Traditionally when a cow has reached the end of her productive life cycle, she is immediately removed from the herd and marketed through a livestock market or sold direct to a packer in her current condition (Yager, Greer, and Burt., 1980). This practice results in many cull cows marketed in poor condition that produces a carcass with inferior characteristics as indicated by the two lowest quality grades, U.S. Cutter, and Canner (Hilton et al., 1996). To compound the problem, the majority of cows are culled in the fall leading to a glut in the cull cow market which translates into low prices. A proposed remedy to both of these problems is to market some cull cows in the spring. An obvious way to carry these cull cows over to the spring is to feed these animals a high-energy diet to improve their body condition as well as their carcass characteristics (Yager et al., 1980; Apple, Davis, Stephenson, Hankins, Davis, and Beaty, 1999). Additional supplementation with a beta-adrenergic receptor agonist has the ability to increase muscle mass and decrease fat mass when fed to growing cattle, producing up to a 25 30% increase in protein accumulation in skeletal muscle (Mersmann, 1998; Bridge, Smith, and Young, 1998). An improvement in carcass characteristics creates value in the boneless subprimals, which would expand the carcass marketing options, currently restricted to ground beef and sausage manufacturing (Hilton et al., 1996). 12

PAGE 13

13 CHAPTER 2 LITERATURE REVIEW Forage Diet Brown and Johnson (1991) examined the effect s of energy and protei n supplementation of ammoniated tropical grass hay on the growth an d carcass characteristics of cull cows. During trial 1, which had a feeding period of 118d, 56 Brahma n crossbred cows were assigned to one of four treatments: The control group which was slaughtered at the beginning of the trial to determine initial carcass characteristics Ammoniated hay alone Ammoniated hay plus 2.2 kg dry matter (DM) of liquid cane molasses per day Ammoniated hay plus 2.2 kg DM of citrus pulp per day The feeding trial was repeated using different protein sources. This experiment lasted 110d, and used 63 Brahman crossbred cows were assigned to one of four treatments: The control group which was slaughtered at the beginning of the trial to determine initial carcass characteristics Ammoniated hay alone Ammoniated hay plus 3.4 kg DM of liquid cane molasses per day Ammoniated hay plus 2.9 kg DM of liquid cane molasses plus 0.5 kg DM of cottonseed per day The cows were conditioned to the diets for four days and were weighed for three consecutive days at the beginni ng and end of the trial. Cows fed strictly ammoniated hay consumed a large amount of hay (approximately 3% of their BW). Supplementation of citrus pulp to ammoniated hay reduced ha y intake levels (P < 0.05). F eeding ammoniated hay with the addition of citrus pulp or cane molasses resulte d in a greater (P < 0.05) ADG compared to cows that were only fed ammoni ated hay. ADG did not differ (P > 0.10) between cows fed ammoniated hay plus citrus pulp or ammoniated hay plus molasse s. In trial 2, less (P < 0.05) ammoniated hay was consumed when cows we re supplemented with cane molasses or cane

PAGE 14

molasses plus cottonseed compared to controls. But cows consuming ammoniated hay plus cane molasses or cane molasses plus cottonseed had an increase (P < 0.05) in total feed intake. As expected, ADG improved (P < 0.05) for cows fed ammoniated hay with cane molasses or cane molasses plus cottonseed. Concentrate Diet A more traditional approach to feeding cull cows involves placement in a feedlot on a high energy concentrate diet with or without the use of implants and / or feed additives, like vitamin D3. Wooten, Roubicek, Marchello, Dryden, and Swingle (1979) examined the effect of different dietary energy levels on carcass composition. Cull cows were fed to a constant body condition score using a weight to height (wt:ht) index. Diets included a high energy, moderate energy, and high roughage transitioned to moderate energy. No feeding performance data was reported. Results were given on fat-to-lean mass accretion based on the number of days fed. The authors reported time on feed beyond 63 days resulted in increased fat content in the carcass with no increase (P > 0.05) in amount of lean tissue. Carcass weight gains in realimented range cows were about 75% fat with a 25% increase in lean mass when the feeding period was extended to 108 days. In a similar study, Sawyer, Mathis, and Davis (2004) looked at the effects of feeding strategy on live animal performance and carcass characteristics in cull cows fed three different diets; a conservative treatment (CSV), (conservative treatment consisted of a 30% roughage diet (DM basis) fed for the duration of the study), a moderate treatment (STD), (standard protocol for feeder cattle feed management in the local area (Clayton, NM). This treatment consisted of five diets (30, 25, 20, 15, and 10% roughage) used in a 5 day adaptation program so that the final diet was fed at the beginning of day 21, and an aggressive treatment (AGR), consisted of a 3 diet (30, 20, and 10% roughage) adaptation program similar to the STD treatment, the diet was changed every five days, but reaching the final diet in half the time). Cull cows managed under the STD 14

PAGE 15

treatment had the highest growth to feed ratio (G:F), whereas the cows managed under CSV treatment experienced the least G:F. Cows under AGR treatment performed intermediate to the other two groups. However during the 29 to 42 day period gain efficiency tended (P = 0.17) to be highest in AGR treatment cows compared to CSV treatment cows which exhibited the lowest gains during this period The different management treatments showed a significant effect on ADG response during the feeding period (P < 0.01). Cows which were managed under STD and AGR treatments gained more (P < 0.01) weight than CSV management cows during the feeding period. Sawyer concluded that even though AGR managed cows were statistically intermediate to STD and CSV, the numeric data indicated that cows fed more energy dense diets (STD and AGR) had superior performance. In addition, it may be beneficial to feed a high-roughage diet for a 5 to 7 day period to optimize intake during the first stages of feeding despite the expense of roughage and the limited time cull cows are on feed. Previous studies also utilized the step-up process by initially starting the cull cows on a higher roughage diet and then gradually building them up to a higher energy diet. In a study conducted by Matulis, McKeith, Faulkner, Berger, and George (1987) growth and carcass characteristics of cull cows fed to different time points was examined. Cows were randomly assigned one of five groups: a control group, a group implanted with Synovex-H2 with the addition of one of four feeding periods (0, 28, 56, or 84). All the cows were initially started out on a 52% corn diet for the first 7 days and then taken up to a 64.5% corn diet the second 7 days of the trial and finally brought up to a 75% corn diet for the remainder of the feeding period. Feed intake for each feeding period increased (P < .05). Daily gain and gain/feed were highest for the 29 56d feeding period. After 56d, the cows had less efficient feed conversion. These results are similar to Sawyer et al. (2004) results without the use of implants. Faulkner, 15

PAGE 16

McKeith, Berger, Kesler, and Parrett (1989) used a similar feeding strategy as Matulis et al. (1987) and examined the effect of testosterone propionate on performance and carcass characteristics of cows. Each group (the control and treatment groups) was fed for two lengths of time, 42 and 84 days. The test group was implanted with 30 cm of testosterone propionate subcutaneously behind the shoulder and over the dorsal aspect of the rib cage. Performance and composition of mature cull cows generally were not influenced by hormone treatment. Additionally most carcass traits were not affected by implanting in this study. Cranwell, Unruh, Brethour, Simms, and Campbell (1996b) investigated the influence of concentrate feeding and steroid implants on performance and carcass composition of mature cull cows. Treatment groups were 1) control, (no implant), 2) 200mg trenbolone acetate (TBA) implant, 3) 200mg testosterone propionate plus 20mg estradiol benzoate (TEB), or 4) both implants (TBA and TEB). The authors reported days on feed increased, final weight, gain, DM intake, ADFI, and fat thickness increased (P < 0.05). Feed efficiency decreased (P < 0.05). Although ADG was similar (P = 0.57) for cows fed for 28 or 56 days, cows fed for 56 days consumed more feed per day, thus resulting in less efficient feedstuff conversion. The animals treated with both implants (TBA and TEB) had (P < 0.05) heavier final weights, more kilograms of gain, and increased gains per kilogram of feed consumed than the control animals. Cows with a single implant of either TBA or TEB tended (P < 0.09) to have the same attributes as the double implanted cows in comparison to control cows. The total DM intake, ADFI, and ultrasound fat thickness were similar (P > 0.10) for all implant groups when compared to the controls across all feeding times. Implanting improved the performance of the cull cows by increasing gains at similar intakes when compared to the non-implanted cows. These results did not support the Faulkner et al. (1989) study. Miller, Cross, Crouse, and Jenkins (1987) looked at 16

PAGE 17

the effect of feed energy intake on collagen characteristics and muscle quality of mature cows fed two different energy level diets for 84d, (a restricted energy intake or an ad libitum plane of nutrition). The authors observed animals gained at a faster rate, and produced heavier carcass weights when fed a high energy diet compared to cows on a maintenance-energy diet which produced carcasses with less fat over the 12 th rib, smaller ribeye area (REA), less kidney pelvic heart fat (KPH) and lower yield grades (YG). Rider Sell, Mikel, Xiong, and Behrends (2004) studied the effect of vitamin D3 supplementation on cull cow performance and carcass parameters. Each cow was randomly selected for one of three highconcentrate diets supplemented with vitamin D3 1) control diet with no vitamin D3, 2) diet supplemented with 5.0 x 10 6 IU of vitamin D3 per cow/per day, 3) diet supplemented with 7.5 x 10 6 IU of vitamin D3 per cow/per day. The diet consisted of 90% corn that was individually fed for 3 weeks before the start of vitamin D3 supplementation, which began on week 4 and was fed until 7 days before slaughter. The authors reported that supplementation did not statistically increase muscle calcium concentrations, muscle calcium levels tended to increase (P = 0.14) numerically with increasing dietary vitamin D3. The study concluded that aging for 14 days had a greater affect on LM tenderness than did treatment with vitamin D3 in cull cows. The majority of cull cow studies conducted typically utilizes days on feed as a constant, while diet or supplementation acts as a variable. However, Schnell, Belk, Tatum, Miller, and Smith (1997) examined the performance, carcass, and palatability traits for cull cows fed a high-energy diet for varied lengths of time (0, 14, 28, 42, or 56 days) on a constant diet. This study revealed that the ADG were negative for the first 14 days of the study but increased through day 28 which agrees with the study reports by Sawyer et al. (2004). Additionally, hot carcass weight, dressing percentage, PYG, and adjusted PYG generally increased (P < 0.05) with the first 28 d of 17

PAGE 18

feeding but remained constant from 28 d to 56 d of feeding. Boleman, Miller, Buyck, Cross, and Savell (1996) examined feeding cull cows different levels of crude protein for different lengths of time to improve meat palatability. The cows were randomly assigned to either a low protein diet (10.21% CP) or a high protein diet (12.82% CP), and fed for 0, 28, 56, or 84 days. Results indicated that feeding a high protein diet did not improve carcass palatability and quality characteristics in mature cows, but can be achieved more successfully by increasing time on feed, feeding a lower protein diet. Optaflexx Regiment An ulterior approach with concentrate feeding would be supplementation with a beta adrenergic receptor agonist, (Optaflexx) with or with out the addition of an implant to improve feeding and carcass performance. Van Koevering et al. (2006b) examined the effect of Optaflexx (RAC) on steers (n=1,867) when fed for the final 28, 35, or 42 days (DUR) of the finishing period. RAC was fed at approximately 0 (CON), 100 (LOW), and 200 (HIGH) mg/hd/day. There were no differences in RAC x DUR interaction (P > 0.62) in regards to live performance, as well as no differences (P > 0.07) in feed intake for either level of RAC compared to CON. Steers fed either RAC treatments experienced greater (P < 0.0001) average daily gain (ADG), as well as improved (P < 0.0001) feed efficiency for both LOW and HIGH RAC dosages. The carcass weights of steers fed at the LOW and HIGH RAC dosage were heavier (P < 0.0001) than CON, had decreased (P < 0.002) calculated yield grade, increased (P < 0.0001) ribeye area (REA), and carcass conformation scores. A RAC x DUR interaction (P < 0.07) was observed with the greatest response from the HIGH RAC level for 42 day carcasses. In a similar study conducted by Crawford, Erickson, Vander Pol, Greenquist, Folmer, and Van Koevering (2006) that looked at the effect of RAC dosage (0, 100, and 200 mg/hd/day) and DUR (final 28, 35, or 42 days of feeding) on English x Continental steers (n = 859). All animals 18

PAGE 19

received the same diet for the duration of the study. Dry matter intake (DMI) linearly decreased slightly (P = 0.01) as RAC dosage increased. Also, ADG increased (P < 0.001) as RAC dosage increased. The reduction in DMI and the increase in ADG, caused the gain to feed ratio (G:F) to improve (P < 0.001). DMI, ADG, or G:F was not impacted (P > 0.38) by DUR or RAC dosage. Also, no RAC dosage x DUR interaction (P > 0.58) occurred for live performance. Carcass weight increased (P < 0.01) as RAC dosage increased, but there was no affect (P > 0.38) on carcass characteristics, and no RAC dosage x DUR interaction (P > 0.58). Greenquist, Vander Pol, Erickson, Klopfenstein, and Van Koevering (2006) also evaluated the effects of RAC on crossbred feedlot steers. Treatments were assigned to pens after re-implanting (82d) which consisted of 0 or 200 mg/hd/day of RAC for 28 or 42 days prior to harvest (DUR). All steers were projected to be harvested at 179 days of feeding with the exception of steers fed RAC for 42 days which would be harvested on day 193, 14 days after the first harvest date. RAC dose x DUR interactions were not found (P>0.44) for live animal performance. ADG numerically decreased (P = 0.07) with the increase of DUR of 14 days. In addition, final BW also increased (P < 0.01) along with an increase (P = 0.02) in DMI causing a reduction (P < 0.01) in weight gain efficiency by extending the finishing period by 14 days. Extending DUR by 14 days resulted in heavier (P < 0.01) HCW, greater dressing percents (P < 0.05), REA, KPH, and 12th rib fat thickness (P < 0.01). Again, in a similar study by Schroeder, Polser, Laudert, Vogel, Ripberger, and Van Koevering (2003a) the effects of RAC dosage (0, 100, 200, or 300 mg/hd/day) and DUR (final 28 or 42 days of feeding) were evaluated in Continental x British, Hereford, Angus, Hereford x Angus, and Brangus x Angus heifers (n = 860) and steers (n = 880). Animal diets were supplemented with Rumensin, Tylan, and MGA, but were not fed during the final 28-42 days while RAC was fed. In addition to feed 19

supplemented RAC at the rate of 0.41 mg/kg of body weight for the last 32 days of feeding. Heifers were randomly assigned to pens (n = 8 pens with 6 heifers per pen) and half of the animals in each pen were randomly selected for ovariectomization (OVX). Cattle were implanted with Component TEIH and fed for 130 days (group 1; n = 4 pens) and 144 days (group 2; n = 4 pens). Heifer ADG, average daily feed intake (ADFI), and G:F was not affected by RAC or OVX. RAC fed heifers had a higher (P < 0.01) dressing percent compared to controls, and HCW, chilled carcass weight (CCW), and REA tended (P < 0.10) to be increased by feeding RAC. Dressing percents were higher (P < 0.01), and REA was larger (P = 0.05) for intact heifers. Intact heifers also tended to have older (P = 0.09) bone maturity scores and lower (P = 0.09) yield grade than OVX heifers. Holmer, Holmer, Berger, Brewer, McKeith, and Killefer (2006) examined beef cows (n = 60) fed three different diets; maintenance diet (CON), 80% concentrate diet (FED), and FED diet with the addition of 200 mg/hd/day of RAC for the last 35 days of feeding (OPTA). One pen from each treatment was harvested after 57 days on treatment over a four week consecutive period. Live weights and ADG were lower (P < 0.05) for CON cows compared to FED cows for the duration of the trial. FED cows increased (P < 0.05) in HCW, REA, KPH, marbling, quality grade, adjusted fat thickness, and yield grade while yellow fat color decreased (P < 0.05) versus CON cows. With the addition of RAC, improvements (P < 0.05) for lean maturity scores and improvement trends (P > 0.05) for HCW, dressing percent, and REA were observed compared to FED cows. A similar study by Kutzler, Holmer, Leick, McKeith, and Killefer (2006) examined beef cows (n = 14) that were fed for 57 days on one of three diets; forage maintenance (CON), high energy concentrate (FED), or high energy concentrate with RAC fed for the last 35 days before harvest (OPTA). The CON treatment had lower (P < 0.05) HCW in comparison to the 21

PAGE 22

FED treatment group. However there were no differences in FED versus OPTA treatment groups for HCW. CON was higher (P = 0.02) than the FED in muscle protein from the LM (mg protein / g dry tissue), but there was no difference between the FED and OPTA groups (P = 0.98) Muscle Histology Limited research has been done in aged cattle focusing on muscle histology. Skeletal muscle mass loss and function occurs with aging. This loss of skeletal muscle mass is known as sarcopenia (Greenlund and Nair, 2003; Carmeli, Coleman, and Reznick, 2001; and Morley, Baumgartner, Roubenoff, Mayer, and Nair, 2001). Type IIa muscle fibers in particular are subject to disproportionate atrophy as a result from decreased protein synthesis with steady protein degradation (Greenlund and Nair, 2003; Carmeli et al., 2001; and Morley et al., 2001). Young cattle (bulls, heifers, and steers) that have been supplemented with a beta adrenergic agonist (Ractopamine-HCl, Cimaterol, Clenbuterol, and L644,969) had been shown to have hypertrophic effects on type II muscle fibers as well as increased protein synthesis compared to control cattle (Vestergaard, Henckel, Oksbjerg, and Sejrsen, 1994; Wheeler and Koohmaraie, 1992; Eisemann, Huntington, and Ferrell, 1988; and Miller et al., 1988). A study conducted by Gonzalez, Carter, Johnson, and Johnson (2006) examined the effects of feeding Ractopamine on LM fiber area and diameter of cull cows. Culled crossbreed beef cows (n=92; 11 yr 1.8) were fed a basal diet for 90d in one of four treatment groups; the control group (CON) received only the basal diet for 90d; the implant group (IMP) received the basal diet for 90d plus an implant treatment (trenbolone acetate plus estradiol); ractopamine group (RAC) received the basal diet for 55d and for the final 35d of feeding received the basal diet plus ractopamine (200 mg/hd/d); and the implant supplemented with ractopamine group (IMP X RAC) received the same regiment as the RAC group but with the addition of an implant. On day 92 of the experiment the animals were harvested and LM samples were collected and analyzed. Results reveled a 22

PAGE 23

significant (P < 0.01) treatment by implant interaction for both area and diameter. The IMP X RAC group had significantly (P < 0.05) larger area and diameter muscle fiber measurements compared to the CON, IMP, and RAC groups. Warner-Bratzler Shear Force (WBSF) One of the largest problems with the palatability of fresh beef from mature cull cows is product tenderness. An inverse relationship exists between carcass maturity and tenderness (Boleman et al., 1996). Typically, subprimals from mature carcasses require mechanical or enzymatic tenderization. Feeding cull cows a high energy diet may help to enhance tenderness. Previous studys conducted by Matulis et al. (1987), Miller et al. (1987), and Boleman et al. (1996), support the concept that feeding increases tenderness reported from WBSF values of the LM. Matulis et al. (1987) reported WBSF values decreased for the latter two feeding groups (56 and 84 days) compared to the first two feeding groups (0 and 28 days). Boleman et al. (1996) found that shear force values of the LM showed a significant (P < 0.05) interaction between time on feed and postmortem treatment. The shear force values of the LM decreased by 3.2 kg with longer periods on feed from 0 to 84 days. The authors also found that fat thickness and shear force were significantly (P < 0.01) correlated (-0.36), it is likely that part of the reduction in shear force was due to the increase of fat thickness causing a reduction in cold shortening. Miller et al. (1987) reported pre-slaughter feeding also reduced shear force values but from increased percent of heat liable collagen contributing to the reduction in stability of intermolecular collagen crosslinks. In related studies by Brown and Johnson (1991), cull cows fed ammoniated hay had lower (P < 0.06) shear values compared to the controls. Rider Sell et al. (2004) found a vitamin D3 and aging period interaction (P < 0.05). Vitamin D3 had no effect on WBSF values for unaged steaks; however, after 7 day aging period LM steaks from cows fed 7.5 x 10 6 IU/day vitamin D3 had lower shear force values compared to steaks from the controls 23

PAGE 24

and 5.0 x 10 6 IU/day vitamin D3. In contrast, steaks aged for 14 and 21 days from cattle supplemented with 5.0 x 10 6 IU/day vitamin D3 had greater (P < 0.05) WBSF values than steaks from the controls. Cattle that were supplemented with the 7.5 x 10 6 diets were not different (P > 0.05) from the controls. Cranwell, Unruh, Brethour, and Simms (1996a) found that even though LM WBSF values were not statistically different (P = 0.51) for implant versus the control cows a trend did exist for cows implanted with TBA to have lower WBSF values followed by steaks from cattle supplemented with TBA plus TEB, TEB, and controls. WBSF values for LM steaks were more acceptable (P < 0.05) at 42 days than 0 days on feed (Faulkner et al., 1989). There was no further advantage in feeding cows for 84 days. However LM steaks from animals treated with testosterone showed no effect on WBSF values. Results by Schnell et al. (1997) also stated that there was no difference (P > 0.05) in WBSF values across a 56 day feeding period with no implant treatments. Holmer et al. (2006) extracted ten muscles (Serratus ventralis, Complexus, Longissimus dorsi, Psoas major, Gracilis, Semimembranosus, Adductor, Pectineus, Rectus femoris, and Vastus lateralis) from each side 72 hours postmortem. Muscles from one side of each carcass were enhanced with a salt phosphate solution and aged for 13 days. Minimal differences were observed for WBSF due to diet (CON, FED, OPTA). The Adductor did not decrease (P>0.05) in WBSF value due to enhancement. The Schroeder, Polser, Laudert, and Vogel (2003b) study reported WBSF evaluation conducted on 2.54 cm thick strip loin steaks (n = 720) cooked to a medium degree of doneness (70 C) from young (A maturity) steers and heifers treated with 0, 100, 200, 300 mg/hd/day of RAC. WBSF values were 4.0 kg or less for all treatment groups. No differences were observed (P > 0.45) when comparing controls to the 100 and 200 mg/hd/day RAC treatments, but WBSF values for the 300 mg/hd/day treatment group was increased (P < 0.05) compared to controls. 24

PAGE 25

Soluble Collagen Miller et al. (1987) found that increased dietary energy levels resulted in an increase (P < 0.05) in the percentage of newly synthesized heat labile collagen and reduced the proportion of insoluble collagen. Schnell et al. (1997) found similar results stating that soluble collagen content within the LM increased (P < 0.05) as time increased while feeding a high energy diet. But once 28 days on feed was achieved, collagen synthesis reaches a plateau. Cranwell et al. (1996a) supports Schnell et al. (1997) findings that percent soluble collagen increased (P < 0.05) for cows fed from 0 to 28 days, but no change occurred for the 28 and 56 day period. Cranwell et al. (1996a) also found that cows implanted with TBA and TEB had more (P < 0.05) LM soluble and percentage of soluble collagen than controls. Boleman et al. (1996) also reported that percent soluble collagen increased with time on feed, and that cows fed for 84 days had less (P < 0.03) detectable connective tissue than cows fed for 0, 28, or 56 days. And Rider Sell et al. (2004) found that collagen content in the loin muscle and semitendinosus was not (P > 0.05) different between both vitamin D3 treatment and aging groups. Myofibrillar Tenderness Schnell et al. (1997) found that cows fed for 56 days had higher overall sensory panel tenderness scores (P < 0.05) than cows fed for either 0 or 14 day periods. Cranwell et al. (1996a) found results that support Schnell et al. (1997) study that higher (P < 0.05) taste panel scores for myofibrillar tenderness were achieved when cows were fed for 28 days or 56 days. They also stated that sensory panel scores increased in overall tenderness when steaks from fed cows were compared to non fed cows and could be attributed to a slight increase in myofibrillar tenderness and a decrease in detectable connective tissue amounts. Fed cows with implants produced steaks with higher (P < 0.05) sensory panel scores for myofibrillar tenderness compared to steaks from fed non-implanted cows (Cranwell et al., 1996a). LM steaks from TBA implanted cows had a 25

PAGE 26

higher (P < 0.05) myofibrillar tenderness sensory panel rating compared to TEB and TBA plus TEB implanted cows. Holmer et al. (2006) observed with enhancement of cow muscles tenderness increased (P <0.05). The Schroeder et al. (2003b) study observed at the 100 and 200 mg/hd/day RAC levels, no differences (P > 0.38) were detected for initial and sustained tenderness, but at 300 mg/hd/day of RAC initial and sustained tenderness values for LM steaks were lower (P < 0.05) compared to controls. Marbling Marbling plays a large role in the marketability of mature carcasses. Feeding cull cows a high energy diet should increase the marbling scores of these carcasses, thus yielding an improved USDA quality grade. Multiple studies support the theory that feeding a high energy diet to cull cows will in fact allow those cows to deposit more intramuscular fat. Marbling scores did increase (P < 0.05) between 28 and 56 days of feeding, however, no differences were observed between 56 and 84 days on feed (Matulis et al., 1987). Faulkner et al. (1989) reported marbling scores increased (P < 0.05) with time on feed. Wooten et al. (1979) reported in trial 1 and trial 3 of their study marbling scores increased (P < 0.05) for cows on feed. Increases in marbling seemed to be primarily associated with length of time on feed and not the level of concentrate in the diet. Sawyer et al. (2004) found that marbling did increase in fed cattle but there was an age relationship with amount of marbling. They reported that marbling scores were related quadratically to age (P = 0.02), with middle-aged cows marbling higher than younger or aged cows. Brown and Johnson (1991) reported greater (P < 0.01) amounts of marbling, leading to higher (P < 0.01) USDA quality grades when cows were fed ammoniated hay either alone or with citrus pulp or molasses than the control cows. Additionally, these authors reported that ammoniated hay supplemented with molasses or molasses plus cottonseed meal fed to cows resulted in slightly higher (P < 0.10) marbling scores, and greater (P < 0.01) USDA quality 26

PAGE 27

grades compared to ammoniated hay alone. Interestingly, Schnell et al. (1997) did not find an affect (P > 0.05) of marbling with increased time on feed (14, 28, 42, and 56 days) when compared to non fed cows. Shroeder et al. (2003b) observed that RAC had no effect on marbling (P > 0.32, steers; P > 0.54, heifers) and quality grade (P > 0.29, steers; P > 0.55, heifers). Similar results were observed by Van Koevering et al. (2006a) stating RAC levels had no effect (P < 0.21) on marbling score in A maturity steers. Talton et al. (2006) also observed marbling scores were not affected by ovariectomization or RAC. Greenquist et al. (2006) observed evidence supporting similar studies stating that by extending RAC feeding duration from 28 to 42 days did not result in higher (P = 0.54) marbling scores. Flavor Because a beef cow is generally raised on pasture all her life, there is a tendency for the meat to develop off-flavors associated with grass feeding. Feeding cull cows a high concentrate diet may help reduce some of these off-flavors making their meat more acceptable. LM steaks from cull cows fed a high concentrate diet for 28 or 56 days had (P < 0.05) higher taste panel scores for flavor intensity in comparison to non fed cows (Cranwell et al., 1996a; Boleman et al., 1996). The increase in sensory panel rating for flavor is partially attributed to feeding, thus a more desirable grain-fed flavor. Cranwell et al. (1996a) reported sensory steaks that were evaluated for the 28 to 56 day fed period were rated in the ranges of acceptable. Flavor intensity among all implant treatments scored similarly (P < 0.05). Faulkner et al. (1989) reported an increased beef flavor intensity and desirable flavor (P < 0.05) at 42 days with no additional benefit in flavor feeding to 84 days. However, the authors did find that off-flavor ratings tended to be higher for testosterone treated animals (P < 0.10). Schnell et al. (1997) did not reach similar results compared to the other studies. They found that sensory panel flavor attributes (cooked beefy brothy, cooked beef fat, cowy/grainy, liver, serum/bloody, and metallic) did not 27

PAGE 28

differ across time-on-feed group. Also, flavor intensity scores did not differ (P > 0.05) for LM steaks over the different feeding period groups. In the Rider Sell et al. (2004) study feeding vitamin D3 they found LM steaks aged for 7 days had no differences (P > 0.05) in beef flavor intensity and off-flavors between treatment groups (vit D3 and controls). There were also no differences in flavor intensity or off-flavors in the 21d aged steaks. Additionally, steaks from cows fed 7.5 x 10 6 IU/d of vitamin D3 had higher (P < 0.05) off-flavor ratings than steaks from cows fed 5.0 x 10 6 IU/day of vitamin D3. Holmer et al. (2006) observed muscles that were enhanced caused sensory beef flavor intensity and off-flavor to increase (P < 0.05). Schroeder et al. (2003b) examined the sensory attributes of strip loin steaks from steers and heifers fed a concentrate ration supplemented with RAC and observed minimal numbers of samples exhibiting off-flavors, resulting in very low off-flavor scores. RAC treatments did not exhibit any differences (P > 0.05) for flavor or off-flavor. Juiciness Faulkner et al. (1989) found that steaks from cows fed for 42 days or longer were more desirable (P < 0.05) in juiciness than steaks from cows fed for 0 days. There was no further benefit in steaks from cows fed for 84 days, in addition sensory scores for juiciness tended to be higher for testosterone-treated animals (P < 0.10). Cranwell et al. (1996a) sensory evaluations determined that steaks were juicier and in the ranges of acceptability from cows fed during the 28-56 day time period. Also, the sensory panel scored steaks from the TBA implanted cows as juicier (P < 0.05) than from the cows that were implanted with TEB and controls. Schnell et al. (1997) and Rider Sell et al. (2004) found no statistical differences in juiciness compared to treatment animals and controls. Holmer et al. (2006) observed muscles that were enhanced with a salt phosphate solution increased (P < 0.05) in juiciness compared to non-enhanced muscles. 28

PAGE 29

Schroeder et al. (2003b) reported that RAC treatments did not exhibit any differences (P > 0.05) in juiciness. Color To consumers, color is a very important characteristic when deciding to purchase food products. One of the challenges in marketing mature cow beef is altering the lean and fat color from dark red with yellow fat to cherry red with white fat. In general, as age increases lean color values tend to be darker and fat tends to be more yellow (Sawyer et al., 2004). Feeding a high energy diet may be a way to alter those two tissue colors. In the study conducted by Boleman et al. (1996) carcasses from fed cows during the 56 day period had the whitest (P < 0.05) fat color, and cows on 0 days of feed had the least (P < 0.05) desirable lean color. Studies from Cranwell et al. (1996a), Matulis et al. (1987), and Schnell et al. (1997) all reported similar results stating as time on feed increases fat and lean tissue color tend to become more white and a brighter cherry red color, respectively. Cranwell et al. (1996a) and Matulis et al. (1987) found that the lean color changed to a brighter (P < 0.05) cherry red color for the cows that were fed for 56 days, and Schnell et al. (1997) found that fat color became more (P < 0.05) white by day 28. Brown and Johnson also found similar results showing that feeding cows ammoniated hay supplemented or not with a protein source for approximately 100 days produced a whiter (P < 0.05) fat color. They also found that cows which were fed citrus pulp had darker (P < 0.05) lean compared to cows supplemented with cane molasses. Additionally, they found that ammoniated hay supplemented with molasses or molasses plus cottonseed meal produced whiter (P < 0.01) subcutaneous fat compared to cows fed ammoniated hay alone. They found no interactions between molasses alone and molasses plus cottonseed meal. Holmer et al. (2006) observed minimal differences for color due to diet (CON, FED, OPTA). Similar results were reported with Talton et al. (2006) stating color was not affected by RAC or ovariectomization. In 29

PAGE 30

contrast, Schroeder et al. (2003) reported results stating RAC at all dosage levels (100, 200, and 300 mg/hd/day) improved (P < 0.06) muscle color in steers and heifers. Objective Future work that could be examined in order to improve cull cow salvage value would be to observe the affect of feeding cull cows a concentrate diet for 54 days with ractopamine-HCl fed the final 30 days of the feeding period at levels of 100, 200, and 300 mg/hd/day to determine if there is a dose affect when supplementing with ractopamine-HCl. A titration study would be valuable because past studies predominately compare ractopamine supplementation at a single level to animals not fed, or fed for varying durations throughout the study. Prior studies concentrated mainly on the LM to determine meat quality. Key muscles from the chuck and round with the addition of the LM will be extracted from carcasses in order to determine effects on meat quality to determine if selected muscles could potentially add greater value to the carcass. With limited histological data available, samples will be extracted from four muscles in order to determine any changes in the muscle at the cellular level to better understand any gross effect that might occur. Finally, it would be valuable to producers in Florida to determine the economic viability of feeding cull cows apposed to marketing them in thin condition. 30

PAGE 31

CHAPTER 3 FEEDING OPTAFLEXX TM (RACTOPAMINE HCL) TO CULL COWS: EFFECTS ON CARCASS COMPOSITION AND YIELD Introduction Cull cows, a by-product of the cow-calf industry, can represent 10-20% of a producers income. Often times these mature animals are marketed due to failure to conceive, health, or structural related problems. These animals are typically marketed when they are in their poorest condition causing the producer the inability to capture the full salvage value of the animal. Previous research shows that feeding cull cows a concentrate diet will increase hot carcass weights (HCW), longissimus muscle area (LMA), intramuscular fat (IMF), subcutaneous fat, and fat-free soft tissue (Wooten et al., 1979; Matulis et al., 1987; Miller et al., 1987; Faulkner et al., 1989; Cranwell et al., 1996b; Schnell et al., 1997). Additional supplementation with a beta adrenergic receptor agonist (ractopamine-HCl) has the ability to increase muscle mass and decrease fat mass when fed to growing cattle, producing up to a 25 30% increase in protein accumulation in skeletal muscle (Mersmann, 1998; Bridge et al., 1998). Previous studies have also reported that beta-agonist dosage and duration can alter the level of beta adrenergic receptor expression (Eisemann et al., 1988; Mills, 2003). The purpose of this study is to determine if feeding ractopamine-HCl at different titration levels for 30 days will alter carcass composition and yield without negatively affecting carcass quality and tenderness. Materials and Methods Experimental Animals Two truck loads (n=49 each; 10.5 yr 1.2), representing two breed types (Beefmaster, and Angus), of cull crossbred cows were transported from a commercial cow-calf operation in south Florida (Lykes Bros., Okeechobee, FL) to a designated feeding facility in Williston, FL. Upon 31

PAGE 32

arrival, cows were weighed, treated with a pour-on endectocide (Dectomax Pfizer Inc., New York, NY), with the exception of the baseline group (n = 8) which was harvested on day one, and then randomly sorted based on breed type so that each breed was equally represented in each pen. Each animal was fed in one of four pens for 54 days on concentrate feed, and assigned to one of four treatment groups Control fed (CON), Optaflexx TM (RAC) at 100 200 or 300 mg/hd/d. Except for the control, experimental groups received Optaflexx TM during the last 30 days of the 54 day feeding trial. On Day 54, cows were transported to a commercial slaughter facility (Central Packing, Center Hill, FL) and harvested in a conventional manner. Two cows per treatment group were harvested on day one of the trial to identify starting carcass composition; data from those animals were included in appropriate tables, but not analyzed in mean comparisons. Carcass Composition and Yield Measurements At 24 hours post harvest, carcasses were fabricated and nine muscles [adductor (ADD), gracilis (GRA), infraspinatus (INF), longissimus dorsi thoracicus (LM), rectus femoris (REF), semimembranosus (SMB), teres major (TEM), triceps brachii (TRB, TRB LAT, and TRB LONG ), and vastus lateralis (VAL)] were removed (Figure 3-1) and transported back to the University of Floridas Meat Processing Center. Commodity weights were recorded from the select muscles then trimmed to a zero (0.0 cm) fat level in order to determine denuded weights and measurements (max length, max width, and max depth) for dimensional analysis. During the denuding process the TRB was further separated in lateral and long heads. The 9-10-11 rib section was removed according to Hankens and Howe (1946) for compositional analysis. Each muscle was then wet aged at 3.8 2 C for 14 days in a cryovac B2570T (Sealed Air Corp., Duncan, SC) bag then frozen at -40 C. Steaks 2.54 cm thick were cut frozen from the anterior 32

PAGE 33

end of each muscle, with the exception of the TEM and GRA which were utilized in their entirety due to size limitations, for Warner-Bratzler Shear Force (WBSF) determination. Ether extraction was performed on the soft tissue of the 9-10-11 rib section in order to estimate compositional changes of the carcass and ether extraction was performed on a sample of the LM in order to determine percent intramuscular fat (IMF) of the LM. Steaks for WBSF determination were thawed for 18h at 3.8 2 C, and then broiled on a Hamilton Beach HealthSmart 317.5 cm 2 grill (Hamilton Beach / Proctor Silex, Inc., Washington, NC) to an internal temperature of 70C. The steaks were turned once at 35C during cooking. Internal temperature was monitored using a copper constantan thermocouple placed in the geometric center of the steak which was attached to a temperature recorder. The steaks were then chilled for 18h at 3.8 2C in preparation for WBSF core extraction. Six 1.27 cm cores were extracted from each steak parallel to the muscle fiber orientation. Each core was then sheared utilizing a WBSF device (crosshead speed = 200 mm/min) attached to an Instron Universal Testing machine, (Model 1011, Instron Corp., Carton, MA). Statistical Analysis The study was designed as a randomized complete block design with individual animal as the experimental unit. Data was analyzed using PROC MIXED, Least Squares Means procedure of SAS (SAS Institute Inc., Cary, NC, 2003) with a significance level of P<0.05 and trends indicated with an equal sign. There was a significant treatment by muscle interaction for WBSF; therefore means will be presented by muscle across each treatment group for this variable. Results and Discussion Final live weights (Table 3-1) were similar (P > 0.05) across all treatment groups, but a trend was observed for hot carcass weight (P = 0.14) and dressing percent (P = 0.19). Hot carcass weights tended to be heavier for the CON group compared to the 100 and 200 mg/hd/d 33

PAGE 34

treatments with the 300 mg/hd/d treatment having similar hot carcass weights as the CON treatment. Dressing percent was also higher for the CON group in comparison to the 200 mg/hd/d treatment while the 100 and 300 mg/hd/d treatments had similar dressing percentages as the CON treatment. Kutzler et al. (2006) reported no differences in HCW between CON and RAC fed cull cows as well as final live weight, which does agree with this study. In contrast, Talton et al. (2006) reported RAC feeding tended to increase HCW in fed heifers, these findings suggest that mature animals may not be as responsive to a beta-agonist in comparison to younger animals. Mean values for dimensions, commodity weights and denuded weights are presented in Tables A-1 A-5 (appendix A) for each of the ten muscles within each treatment group. The means reported are intended to illustrate size differences between treatment groups for specific muscles. Baseline group was excluded from any statistical analysis, but included in tables to better illustrate dimensional changes which occurred due to feeding. Significant differences (P < 0.05) were observed for commodity weights in the clod, SMB, sirloin tip, and the top round, but when expressed on a percentage of hot carcass weight, no significant differences were noted (Table 3-2). Feeding RAC did not (P > 0.05) alter the carcass weight percentages for any of the muscles evaluated in this study. Ribeye area (Table 3-3) was similar (P > 0.05) for all treatment groups. These findings agree with Holmer et al. (2006), but in contrast Schroeder et al (2003a) reported increased (P < 0.05) REA in young steers and heifers for 300 mg/hd/d treatment groups. When REA is expressed per 100 kg of carcass weight (indicator of muscling) all treatment groups were similar (Table 3-3). 34

PAGE 35

Differences were observed (P = 0.11) in percent fat free lean of the 9-10-11 rib section (Table 3-4) between treatments. The 300 mg/hd/d treatment was 6.3% higher in fat free lean compared to the CON treatment while the 100 and 200 mg/hd/d treatments were intermediate of the CON and 300 mg/hd/d treatments. Higher fed levels of RAC lean accretion is generated at a faster rate than fat deposition. This would be expected considering the active ingredient in Optaflexx TM is a beta adrenergic agonist that redirects nutrients away from fat production and applies those nutrients to lean accretion (Eisemann et al., 1988; Miller et al., 1988; Mersmann, 1998). Percent IMF was not significantly different (P > 0.05) among the treatment groups (Table 3-5). These results agreed with previous studies conducted on heifers (Schroder et al., 2003a; Talton et al., 2006). WBSF data reveals that RAC affects muscles individually (Table 3-6), rather than specific muscle groups such as muscles of locomotion or muscles of support. The INF, REF, SMB, and TRB lat, all had significant (P < 0.05) differences for WBSF across treatment group. WBSF values for ADD, GRA, LM, TEM, TRB long and VAL was not significant (P > 0.05) among treatment group. The INF decreased (P < 0.05) in tenderness with RAC treatment compared to the CON treatment. In contrast, the SMB was higher (P < 0.05) in tenderness at the 100 mg/hd/d treatment compared to the CON treatment. The REF and TRB lat experienced interactions within RAC treatment. The REF in the 100 mg/hd/d group had higher (P < 0.05) WBSF values (less tender) compared to the 200 mg/hd/d group which had lower WBSF values (more tender). The TRB lat had similar results indicating that the 100 mg/hd/d group had higher (P < 0.05) WBSF values in comparison to the 300 mg/hd/d group. Schroeder et al. (2003b) reported WBSF values increased in the LM from young cattle as RAC dosage increased. The data for the REF and TRB lat do not support Schroeder et al. (2003b) findings. The shear values are independent of 35

PAGE 36

cooking degree of doneness and fat which would eliminate inconsistent cooking and cold shortening as potential explanations. Possibly, due to protein turnover, which diluted the existing cross-linked collagen content in the 200 and 300 mg/hd/d treatment compared to the 100 mg/hd/d treatment which would have more cross-linked collagen causing the 100 mg/hd/d treatment to be tougher in muscles of locomotion. This study did not examine collagen content, so speculation can only be applied. In conclusion, feeding RAC at the 100, 200, or 300 mg/hd/d to cull beef cows has little to no affect on carcass characteristics in comparison to feeding with the exclusion of RAC, but RAC did have some minimal affects on total fat-free lean percentage and WBSF values. 36

CHAPTER 4 FEEDING OPTAFLEXX TM (RACTOPAMINE HCL) TO CULL COWS: EFFECTS ON MUSCLE HISTOLOGY Introduction With age, loss of muscle mass, strength and endurance occurs, this is known as sarcopenia. Protein degradation continues at a constant rate with time while protein synthesis slows causing the decline in muscle mass (Morley et al., 2000; Carmeli et al., 2001; Greenlund and Nair, 2002). Postnatal skeletal muscle growth is achieved through the satellite cell (muscle stem cells) population. These normally quiescent cells become mitotically active, proliferate and fuse into existing muscle fibers (Collins, 2006). The number of satellite cells declines with age and the activation potential of these cells are reduced in older individuals (Shefer, Van de Mark, Richardson, and Yablonka-Reuveni, 2006). Beta-adrenergic agonists (ractopamine-HCl, cimaterol, clenbuterol, L644,969) increase muscle accretion by the enhanced delivery of substrates and energy needed for protein synthesis (Mersmann, 1998). In cattle, the mechanism of muscle growth due to ractopamine supplementation is attributed to enhanced protein synthesis (Smith, 1989). Cattle supplemented with a -adrenergic agonist have been shown to induce type II muscle fiber hypertrophy (Eisemann et al., 1988; Miller et al., 1988; Wheeler and Koohmaraie, 1992; Vestergaard et al., 1994). Vestegaard et al., (1994) reported a proportional decrease in type I muscle fibers with an increase in type II muscle fibers revealing that muscle from animals supplemented with a -adrenergic agonist are transitioning from a less oxidative state to more glycolytic. The purpose of this study is to determine if ractopamine supplementation at different titration levels promotes whole muscle hypertrophy, increased cross-sectional area, and diameters of the semimembranosus and vastus lateralis in aged beef cows. 44

PAGE 45

Materials and Methods Experimental Animal Two truck loads (n=49 each; 10.5 yr 1.2), representing two breed types (Beefmaster, and Angus), of cull crossbred cows were transported from a commercial cow-calf operation in south Florida (Lykes Bros., Okeechobee, FL) to a designated feeding facility in Williston, FL. Upon arrival cows were weighed, treated with a pour-on endectocide (Dectomax Pfizer Inc., New York, NY), with the exception of the baseline group which was harvested on day one, and then randomly sorted based on breed type so that each breed was equally represented in each pen. Each animal was fed in one of four pens for 54 days on concentrate feed, and assigned to one of four treatment groups Control fed (CON), Optaflexx TM (RAC) at 100, 200, or 300 mg/hd/d. Except for the control, experimental groups received Optaflexx TM during the last 30 days of the 54 day feeding trial. On Day 54 cows were transported to a commercial slaughter facility (Central Packing, Center Hill, FL) and harvested in a conventional manner. No cows were implanted for this trial. Immunohistochemistry At 24 hours postmortem, following transportation of whole muscles to the University of Florida Meats Laboratory, two 1 cm x 1 cm x 1 cm portions of the semimembranosus (SM), and vastus lateralis (VAL) muscles from 10 randomly selected cows per group (n = 40) were suspended in OCT tissue freezing medium (Fisher Scientific, Hampton, NH). Samples were frozen by submersion in super-cooled isopentane, and stored at -80C. These samples were used for area and diameter measurements, and myosin heavy chain analysis. Two 12 micrometer serial cryosections, one for each fiber type, were collected on frost resistant slides (Fisher Scientific, Hampton, NH) for each sample. Two sets of serial cryosections were collected for each animal. Non-specific antigen sites were blocked in 5% horse serum in phosphate buffer 45

PAGE 46

46 saline (PBS) for 20 minutes at room temperature. Cryosections were incubated for 60 minutes at room temperature in primary antibodies. Antibodies and diluti ons consisted of: -dystrophin (Abcam, Cambridge, MA) 1:500; undiluted supe rnatant myosin heavy chain type 1 (BAD.5, Developmental Studies Hybridoma Bank, University of Iowa, Iowa City, IA); myosin heavy chain type 2A (SC.71, Developmental Studies Hy bridoma Bank, University of Iowa, Iowa City, IA); Pax7 (Developmental Studie s Hybridoma Bank, University of Iowa, Iowa City, IA) 1:5 cultured supernatant. After washing with PBS, tissues were incubated for 40 minutes with goat anti-mouse Alexa FlourPP 568 (1:500; Invitrogen, San Diego, CA) for -dystrophin or goat antimouse biotin (1:100; Vector Laboratories, Burlingame, CA) followed by steptavidin Alexa FlourPP 488 (1:500; Invitrogen, San Diego, CA) fo r Pax7 and myosin heavy chain isoform detection. Following Pax7 immunostaining, Hoechst 33245 (1 g/ml in PBS) was used to identify total nuclei. After a final PBS wash, slides were cover sl ipped and immunostaining was evaluated using an Eclipse TE 2000-U stage microscope (Nikon, Lewisville, TX) equippe d with a X-Cite 120 epifluorescence illumination system (EXFO, Mississauga, Ontario, Canada). Images were captured at 100X magnification using a DXM 1200F digital camera and analyzed for individual muscle fiber area and diameter and total number of fiber associated nucl ei per field using the NIS-Elements computer system (Nikon, Lewisville, TX). For each set of seri al cryosections four images from the same area of each cryosection wa s collected for each myosin heavy chain type (Figure 1). Fibers that were re active with the specific myosin heavy chain type were counted, and fiber cross-sectional area (CSA) was defined as the region constrained by -dystrophin immunostaining. Diameter was measured by the computer system rotating every 90 degrees around the fiber, taking a diameter measurement, and averaging the measurements. For each

PAGE 47

animal, a minimum of approximately 1,000 fibers per animal were measured and used for analysis. Nuclei that were identified with Hoechst dye labeled as Pax7 positive were counted as being a satellite cell. Statistical Analysis The study was designed as a randomized complete block design with individual animal as the experimental unit. Fiber type frequencies were tabulated and compared by chi-square analysis using PROC FREQ of SAS (SAS Inst. Inc., Cary, NC, 2003). Treatment group frequencies within a fiber type were compared to one another by a two sample t-test for proportions. Data for fiber area and diameter were sorted and analyzed by individual fiber type, while fiber-associated nuclei and Pax7 nuclei were not sorted. Results and Discussion Of the two muscles immunohistochemically analyzed for increases in muscle fiber cross-sectional area and diameter (Figure 1), the type I fibers of the VAL muscle increased (P < 0.05) in CSA and diameter, while the SM did not respond (P > 0.05) to RAC supplementation (Table 4-1). For the VAL muscle, RAC treatment significantly effected (P < 0.05) the CSA and diameter of type I fibers with no effect (P > 0.05) on type II fibers. RAC treatments 100, 200, and 300 mg/hd/d increased type I fiber CSA by 38, 56, and 6 percent, respectively, when compared to the CON treatment. The 200 mg/hd/d treatment group had larger (P < 0.05) fiber CSA than the CON and 300 mg/hd/d treatment groups, but was not significantly different (P > 0.05) from the 100 mg/hd/d treatment group. The CON, 100, and 300 mg/hd/d treatment groups did not have significantly different (P > 0.05) fiber CSA. Type I fiber diameter for the 200 mg/hd/d treatment group was significantly larger (P < 0.05) than CON and 300 mg/hd/d treatment groups, but was also not significantly different from the 100 mg/hd/d treatment group. 47

PAGE 48

Skeletal muscle fiber hypertrophy contributes primarily to postnatal muscle growth (Swatland, 1984). Therefore, this indicates that RAC, on whole muscle level, has the inability to stimulate increases in muscle fiber CSA and diameter. When increases in fiber CSA occurred, as in the case of the VAL, only one fiber type was affected or increases in CSA were minimal. Therefore, the increases were not enough to cause increases at the whole muscle level. Few studies reporting increases in type I fiber CSA of cattle fed beta-adrenergic agonists exist. In a previous study conducted by our laboratory (unpublished data) RAC preferentially increased type I fiber CSA of cull cows. Vestergaard et al. (1994) reported 35 percent larger type I CSA in bulls fed cimaterol, a different beta-adrenergic agonist. In general, most studies indicate that beta-adrenergic agonists preferentially increase the CSA of type II fibers, and will also increase type I fibers CSA. This could indicate that the advanced age of these cull cows causes them to react differently and increase in type I CSA. Muscle fiber types were measured using antibodies specific to myosin heavy chain type I and IIA isoforms (Table 4-2). RAC treatment shifted (P < 0.05) the percentage of type I to type II fibers in the VAL at all treatment groups, while the SM experienced a fiber type shift from type I to type II at the 200 and 300 mg/hd/d treatment groups. The exception in the SM muscle resulted from the 100 mg/hd/d treatment group shifting the percentage of fibers from type II to type I. Vestergaard et al. (1994) reported that beta agonists can increase the percentage of type IIA fibers at the expense of type I fibers. Therefore, the shift in fiber type would indicate that successful absorption of RAC occurred even though RAC had a minimal effect on whole muscle and fiber growth. The present studys data indicates that when these muscles are supplemented with RAC, a fiber type shift occurs from type I to type II fibers. The surprising data is that the 48

PAGE 49

100 mg/hd/d treatment group in the SM shifted the fiber type in the opposite direction of the other RAC treatments. Reasons for this shift are unknown and warrant further research. Satellite cells counted per one hundred fibers was measured as an index of muscle fiber hypertrophy due to mitotically active satellite cells. For both muscles, level of RAC supplementation did not affect (P > 0.05) satellite cells detected by immunohistochemistry. These findings support the conclusion that RAC treatment caused CSA increase not the existing satellite cell population. Since RAC supplementation did not increase the detection of satellite cells, we hypothesized that altering of protein synthesis/degradation rate caused the modest increases in fiber CSA seen in the present study 49

CHAPTER 5 OVERALL CONCLUSIONS AND IMPLICATIONS Concluding the 54 day feeding period of mature crossbred beef cows, as described in chapter 3, the final live weights were similar across all treatment groups, but hot carcass weights tended to be heavier for the control fed group compared to the 100 and 200 mg/hd/day treatments with the 300 mg/hd/day treatment having similar hot carcass weights as the control fed treatment. Dressing percent was also higher for the control fed group in comparison to the 200 mg/hd/day treatment while the 100 and 300 mg/hd/day treatments had similar dressing percentages as the control fed treatment. Significant differences were observed for commodity weights in the clod, SMB, sirloin tip, and the top round, but when expressed on a percentage of hot carcass weight, no significant differences were noted. Feeding RAC did not alter the carcass weight percentages for any of the muscles evaluated in this study. Ribeye area was similar for all treatment groups. When REA is expressed per 100 kg of carcass weight (indicator of muscling) all treatment groups were similar. Differences were observed in percent fat free lean of the 9-10-11 rib section between treatments. The 300 mg/hd/day treatment was 6.3% higher in fat free lean compared to the control fed treatment while the 100 and 200 mg/hd/day treatments were intermediates of the control fed and 300 mg/hd/day treatments. Thus showing that at the higher fed levels of RAC lean accretion is generated at a faster rate than fat deposition. This would be expected considering the active ingredient in OptaflexxTM is Ractopamine-HCl which is a beta adrenergic agonist that redirects nutrients away from fat production and applies those nutrients to lean accretion. Percent IMF was not significantly different among the treatment groups which 53

PAGE 54

illustrates that RAC has more of an effect on subcutaneous and intermuscular fat than intramuscular fat or marbling. WBSF data reveals that RAC affects muscles individually rather than specific muscle groups such as muscles of locomotion or muscles of support. The INF, REF, SMB, and TRBlat, all had significant differences across treatment group. WBSF values for ADD, GRA, LD, TEM, TRBlong and VAL was not significant among treatment group. The INF decreased in tenderness with RAC treatment compared to the control fed treatment. In contrast, the SMB was higher in tenderness at the 100 mg/hd/day treatment compared to the control fed treatment. The REF and TRBlat experienced interactions within RAC treatment. The REF in the 100 mg/hd/d group had higher WBSF values (less tender) compared to the 200 mg/hd/d group which had lower WBSF values (more tender). The TRBlat had similar results indicating that the 100 mg/hd/d group had higher WBSF values in comparison to the 300 mg/hd/d group. The shear values are independent of cooking degree of doneness and fat which would eliminate inconsistent cooking and cold shortening as potential explanations. Possibly, due to protein turnover, soluble collagen content(less cross-linking) increased in the 200 and 300 mg/hd/d treatment compared to the 100 mg/hd/d treatment which would have more cross-linked collagen causing the 100 mg/hd/d treatment to be tougher in muscles of locomotion. This study did not examine collagen content, so speculation can only be applied. Of the two muscles immunohistochemically analyzed for increases in muscle fiber cross-sectional area and diameter the type I fibers of the VAL muscle increased in CSA and diameter, while the SM did not respond to RAC supplementation. For the VAL muscle, RAC treatment significantly affected the CSA and diameter of type I fibers with no effect on type II fibers. RAC treatments 100, 200, and 300 mg/hd/d increased type I fiber CSA by 38, 56, and 6 percent, 54

PAGE 55

respectively, when compared to the CON treatment. The 200 mg/hd/d treatment group had larger (P < 0.05) fiber CSA than the CON and 300 mg/hd/d treatment groups, but was not significantly different from the 100 mg/hd/d treatment group. The CON, 100, and 300 mg/hd/d treatment groups did not have significantly different fiber CSA. Type I fiber diameter for the 200 mg/hd/d treatment group was significantly larger than CON and 300 mg/hd/d treatment groups, but was also not significantly different from the 100 mg/hd/d treatment group. When increases in fiber CSA occurred, as in the case of the VAL, only one fiber type was affected or increases in CSA were minimal. Therefore, the increases were not enough to cause increases at the whole muscle level which would help better understand the gross affects from chapter 3. RAC supplementation shifted the percentage of type I to type II fibers in the VAL at all treatment groups, while the SM experienced a fiber type shift from type I to type II at the 200 and 300 mg/hd/d treatment groups. The exception in the SM muscle resulted from the 100 mg/hd/d treatment group shifting the percentage of fibers from type II to type I. The shift in fiber type would indicate that successful absorption of RAC occurred even though RAC had a minimal effect on whole muscle and fiber growth. Satellite cells counted per one hundred fibers was measured as an index of muscle fiber hypertrophy due to mitotically active satellite cells. For both muscles, level of RAC supplementation did not affect satellite cells detected by immunohistochemistry. These findings support the conclusion that RAC treatment caused CSA increase not the existing satellite cell population. Since RAC supplementation did not increase the detection of satellite cells, we hypothesized altering of protein synthesis/degradation rate caused the modest increases in fiber CSA seen in the present study 55

PAGE 56

APPENDIX A DIMENSIONS AND WEIGHTS OF SELECTED MUSCLES FROM NON-FED, FED AND RACTOPAMINE-HCL TREATED CULL COWS Prior to aging, muscles were weighed in order to determine commodity weight then trimmed of all visible fat (0.0 cm) reweighed and measured for dimensional analysis. The Triceps brachii was further separated into the lateral and long heads. Data were analyzed using the PROC MIXED, Least Squares Means procedure of SAS (SAS Institute Inc., Cary, NC, 2003). 56

BIOGRAPHICAL SKETCH Ryan Dijkhuis is a Florida native born on May 22, 1980 in Orlando. He graduated from Deltona high school in 1998 then decided to take time off from school and travel to the Midwest were he worked on a harvesting crew during the 1998 harvest season. Upon his return to Florida he enrolled at Daytona Beach Community College were he earned his Associates of Arts degree in 2002. Following community college he enrolled at the University of Florida in 2003 and earned his Bachelors degree in animal science specializing in beef production. During his undergraduate career he worked at the University of Florida Meat Processing Laboratory, participated on the Livestock and Meat Evaluation team, and engaged in undergraduate research. In addition he was Hazard Analysis Critical Control Point (HACCP) certified. During the summers of 2004 and 2005 he interned at the Roman L. Hruska U.S. Meat Animal Research Center in Clay Center, Nebraska. After graduation he enrolled in the University of Floridas graduate school working under the direction of Dwain Johnson in the Department of Animal Sciences focusing on meat science for his Master of Science degree. During his graduate career he assisted in coaching the 2006 Livestock and Meat Evaluation team, acted as a teaching assistant for undergraduate courses, and assisted with various research projects (NCBA Market Basket Study, 2006; Feeding Cull Cows Ractopamine-HCl II, 2007; NCBA National Market Cow and Bull Quality Audit, 2007; and Veal Muscle Profiling in the Chuck, 2007). 70